1. Field of the Invention
The present invention relates generally to apparatuses for producing high purity oxygen and hydrogen. The present invention also relates generally to methods of producing high purity oxygen and hydrogen. More particularly, the present invention relates to methods and apparatuses for producing high purity oxygen and hydrogen by way of electrolysis of an electrolytic solution.
2. Description of Related Art
In the electronics industry, oxygen and hydrogen of high purity are used, for example, as atmospheric gases for thermal treatment. For instance, in the production process of semiconductors, oxygen of high purity is used as an atmospheric gas for the oxide film formation process, and hydrogen of high purity is used as the atmospheric gas for thermal treatment and for epitaxial growth. The purity of such oxygen and hydrogen impacts the quality of the product. Thus, high purity oxygen and hydrogen are needed in the electronics industry, particularly in the production of integrated circuits. Such gases are produced and provided as described below.
For hydrogen gas, excessive reproduction gas from electrolysis of common salt or from petroleum refinement is first purified by a purifier such as a fractionater, using a PSA (Pressure Swing Adsorption) purification method or a catalytic combustion purification method (primary purification), to obtain somewhat high purity hydrogen. This hydrogen is introduced into a bomb (cylinder), etc. at high pressure and delivered to users.
For oxygen gas, air is liquefied by the Joule-Thomson process, and components of the air are separated from each other by a cryogenic distillation process (low temperature processing), using the differences in their boiling points, to obtain somewhat high purity oxygen. The oxygen thus obtained is delivered in the form of liquefied oxygen to cold evaporators (oxygen gas generators or sources; hereinafter referred to just as "CE") of plants. Liquefied oxygen is vaporized when needed in the gas form.
The gases of oxygen and hydrogen provided by the above-mentioned production methods, however, have impurities such as nitrogen, carbon dioxide, carbon monoxide, hydrocarbons and water (hereinafter referred to as "impurities such as nitrogen"). Such impurities cannot be completely removed by the above-mentioned purifications. Hence, the above-mentioned oxygen and hydrogen must be further individually purified by purifiers at semiconductor plants to remove the impurities (the "secondary purification").
This further purification treatment (the secondary purification) needs to be done by an adsorption treatment with an adsorbent or by a sophisticated purification method such as a palladium membrane permeation process. It is difficult, however, to remove impurities such as nitrogen by the these purification treatment processes. Moreover, semiconductor elements of finer structure and higher strength require an ever-increasing purity of gases for their production, resulting in a requirement of purifiers and purification systems which are very complicated and expensive.
Moreover, oxygen stored in liquid form in CE and hydrogen introduced into and delivered in bombs at high pressure, pose many safety problems in case of emergency, such as earthquakes.
With regard to hydrogen, it is generally assumed that all impurities can be removed by a palladium membrane permeation method. This method, however, poses the problem that carbon contained in the palladium membrane reacts with hydrogen to produce hydrocarbons, which are themselves sources of impurities. Carbon impurities have adverse effects on the production of semiconductors, in particular, on electric properties of oxide films in the production of MOS devices. There is, therefore, a great need to eliminate carbon impurity from hydrogen.
In view of the above, there is a continuing need to develop methods and apparatuses for producing high purity oxygen and hydrogen.